About this replacement
VeriFone CM5P / Carbon Mobile 5 — 3.7V Li-ion Replacement Battery (BPK278-502)
This 3.7V, 5200mAh Li-ion battery replaces the OEM BPK278-502 and BPK278-502-01-A cells in the VeriFone CM5P and Carbon Mobile 5 payment terminals. It fits the original battery bay and connects to the same BMS contacts as the factory cell. Capacity figures come from the product data — 19.24Wh total stored energy.
- CM5P and Carbon Mobile 5 fitment: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. Swapping between them requires no adapter or modification — the voltage rail and communication lines are identical across the two variants.
- Bench tested on actual hardware: We cycled this cell through charge, idle, and active transaction loads. The BMS accepted the handshake on first boot, held the voltage rail steady through printer-motor draw spikes, and engaged protection cutoff correctly at the low-voltage threshold.
- First-deployment cycle on the CM5P: After fitting the battery, complete at least one full power cycle — boot the terminal, run a test transaction, and let the charge indicator update. The CM5P maps battery capacity during normal operation, and the charge gauge will not read accurately until the terminal completes that calibration cycle.
Terminal rebooting mid-transaction after a battery swap
The CM5P draws a sharp current spike when the receipt printer fires. On a new cell, the BMS has not yet learned the load profile of this terminal, so it can interpret that spike as an overcurrent event and trip the protection circuit. This cuts power for roughly one second — long enough to force a reboot mid-sale. Running five to ten complete transaction cycles, including receipts, trains the BMS to recognise the printer load as normal and stops the false trips.
Battery indicator stuck at 99% after the first full charge
A new lithium cell arrives at a partial state of charge, and the CM5P's charge IC enters top-off mode on the first charge rather than a full constant-current sweep. The gauge firmware reads this as 99% because it has not yet recorded a complete charge curve from the new cell. This is not a faulty battery or a faulty charger. Discharge the terminal through normal use until it auto-shuts down, then charge to 100% uninterrupted — after that cycle the indicator will read correctly.